This interactive Research Project Grant (IRPG) will address autonomic nervous system (ANS) influences on cardiorespiratory transition during the evolution from fetal to neonatal life by using spectral and nonlinear analysis of heart rate variability (HRV). The overriding objective in the companion application titled "Spectral and Nonlinear Analysis of the Fetal Heart Rate" is to identify any alterations of the power spectral density (PSD) during labor and delivery, and correlative or predictive patterns that may aid the obstetrical/neonatal health care provider in the recognition of the fetus on neonate predestined for untoward events. The main objective of this application is to examine the differences/similarities in HRV in the same individual as she experiences labor, delivery (fetus_neonate), birth, and the first ten hours of extrauterine life. The aims are to: (1) determine the natural history of HRV exhibited as the fetus experiences labor and delivery, and subsequent transition to extrauterine life as a neonate; (2) identify patterns of HRV, respiratory rate variability (RRV), blood pressure variability (BPV) and skin temperature variability (TV) in both pre- and full-term healthy and high-risk infants with successful and unsuccessful transition over the first ten hours of life; (3) determine the correlation between standard methods of neurophysiologic assessment and the PSD as the neonate experiences the first 10 hours of life; (4) analyze the effects of obstetric confounders (i.e. analgesia, maternal complications) on neonatal HRV; and (5) redefine the two periods of reactivity in the pre- and full-term healthy and high-risk neonate during the first ten hours of life. A prospective, repeated measures, time series design will be used to compare and contrast the physiologic variability from in utero to extrauterine life. Spectral and nonlinear time series techniques will be used to capture and examine the complex, fractal dynamics occurring as the fetal-neonatal physiology is changing in time as they relate to ANS influences. It is anticipated that the use of this advanced technology will strengthen clinical practice due to an enhanced ability to better evaluate neurophysiologic indicators of stability of both the healthy and compromised fetus and neonate.